The major objective is to conduct a cross-sectional and longitudinal study of auditory function in aging human subjects, and in aging-human subjects who have a well-documented history of noise exposure. The major purposes are to specify categories or profiles of presbyacusis, and to compare aging, noise exposed persons with aging, non-noise exposed persons. A large number of auditory and non-auditory measurements will be made including evoked potentials and clinical chemistries. In a human experiment which parallels an animal experiment from Project #1 we will examine amplitude-intensity and latency-intensity functions of evoked potentials arising from the auditory nerve, brainstem, and cortex of aging human subjects. Data will be analyzed in relation to loudness data obtained by direct magnitude estimations. In a third set of experiments the age- related decline of frequency selectivity will be assessed psychophysically using a masking paradigm, and physiologically using the same masking paradigm and evoked potentials arising from the auditory nerve, brainstem, and cortex. A similar evoked potential experiment is planned in Project #1. Our experimental approach, which combines psychophysical and physiological data with clinical information will provide novel insights into age-related hearing loss and noise-induced hearing loss. We fully expect the results to contribute to diagnostic and rehabilitative procedures as well as to theoretical issues in audition.